Lateral force resisting system

ABSTRACT

A moment frame is formed with two vertical T-shaped posts connected by several cross members secured perpendicular to the two posts forming a ladder-like frame. The cross members are formed of hot rolled steel and are permanently welded to cutouts in the posts. The top of the moment frame is attached to the building structure using any suitable mounting components. The base or bottom of the moment frame is attached to the foundation, or floor using any suitable mounting components.

RELATED APPLICATIONS

This application claims priority from copending U.S. Provisional PatentApplication 61/930,374 filed Jan. 22, 2014.

FIELD OF THE INVENTIONS

The inventions relate generally to the field of building constructionand in particular to structural framing elements for buildingconstruction.

BACKGROUND OF THE INVENTIONS

Buildings are subjected to many forces. Among the most significant aregravity, wind, and seismic forces. Gravity is a vertically acting force,wind and seismic forces are primarily lateral (horizontal). Manybuildings use shearwall diaphragms columns and other structural elementsto resist lateral loads. Conventional shear resistive building elementsare formed by the application of one or more types of sheathing such as,plywood, fiberboard, particleboard, and or drywall (gypsum board), tothe inside or outside or both sides of a wall frame. The sheathing isfastened to the wall frame at many points creating a shearwall diaphragmor panel. Many suitable fasteners are available and nails are commonlyused and will be referred to hereafter. The sheathed shearwall panel isused to conduct the lateral force acting on the frame of the building tothe foundation.

Another misconception among the designers of conventional buildings isthe illusion that stiffer is better where lateral force resistance isdesired. For example, in some buildings the lateral force resistance isprovided by steel I-beams or rigid steel trusses secured in thefoundation. In an earthquake the very stiff I-beams and trussesexperience catastrophic failure leading to building collapse.

Conventional manufacturers of wood and metal shear resistive buildingcomponents continue to add elements and stiffness to their products totry and eliminate ductility or flex in their products. As a result, mostconventional manufactured shear resistive building components experiencecatastrophic failure when developing their maximum shear resistance.

SUMMARY

The devices and methods described below provide for a moment framehaving two vertical T-shaped posts connected by several cross memberssecured perpendicular to the two posts forming a ladder-like frame. Thecross members are formed of hot rolled steel and are permanently weldedinto cutouts in the posts. The top of the moment frame is attached tothe building structure using any suitable mounting components. The baseor bottom of the moment frame is attached to the foundation, or floorusing any suitable mounting components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a steel moment frame.

FIG. 2 is a cross section of the steel moment frame of FIG. 1 takenalong A-A.

FIG. 3 is a front view of a post from the steel moment frame of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 illustrates moment frame 10 which includes first post 11 andsecond post 12 which are connected together by cross members 13. Firstpost 11 and second post 12 have a “T” cross section as illustrated inFIG. 2. Post webs 11W and 12W may be notched to accommodate the crossmembers as shown in FIG. 3. Cross members or bars such as cross members13 are preferentially inserted and welded into notches 14 to keep theframe symmetric and thus reduce the amount of weld needed because crossmembers 13 are locked in by compression instead of placing the welds inshear. Cross members 13 may be attached to post webs 11W and 12W usingany suitable technique. Any suitable cross section of cross members 13may be used such as solid, hollow, tube, round, square, rectangle, “I”or “C” shaped. Naturally rectangular shapes are prone to compressionside buckling and cross member needs to have sufficiently thick walls tokeep the wall from bulking or collapsing. The closer the plastic modulusof the cross members matches the elastic modulus the less the backbonewill curve in the transition from elastic to plastic. A reduced sectioncould be used to insure a more precise bending location.

The components of moment frame 10 may be formed of any suitable ductilemetal. For example, cross members 13 may be formed of hot rolled steelto improve ductility of the moment frame. If the shear value of thecross members is held constant the moment frame or panel will be stifferthe larger the cross member or bar so long as web 11W of the post cantake the moment of the cross member. Likewise, moment frame 10 will bestiffer with hot rolled metal as apposed to a higher strength formation.Typically hot rolled has enough strain capacity that one can design thissystem as a simple cantilever column and size the cross members or barsto resist the shear.

Any suitable moment connections can be made first end 10T or second end10B to create a stiffer system. Other column sections could be usedinstead of a “T”. A “T” shaped post represents an efficient use of themetal but if there is a significant dead load on the post then eitherthickening the “T” section or going to a closed section such as a tubemay be necessary. Typically the post should be designed to stay elastic.If the post starts to buckle a more pinched hysteresis will occur. Anysuitable shape connector 15 may be secured to first end 10T forattaching the panel to most any framing condition.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Theelements of the various embodiments may be incorporated into each of theother species to obtain the benefits of those elements in combinationwith such other species, and the various beneficial features may beemployed in embodiments alone or in combination with each other. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

We claim:
 1. A moment frame comprising: two coplanar vertical sidemembers, each vertical side member having an inside web and an outsidesurface; a plurality of lateral force resisting members secured to theinside webs between the vertical side members forming a plurality ofgenerally rectangular openings therebetween, wherein the lateral forceresisting members control rigidity and resist lateral forces applied tothe structural frame; and a plurality of holdown attachment points onthe outside surface of each vertical side member.
 2. The moment frame ofclaim 1 wherein the plurality of lateral force members are generallyright circular cylinders formed of hot rolled steel.